Moshing (also known as slam dancing or simply slamming) is an extreme style of dancing in which participants push or slam into each other. Taking place in an area called the mosh pit (or simply the pit), it is typically performed to aggressive styles of live music such as punk rock and heavy metal.

The dance style originated in the southern California hardcore punk scene, particularly Huntington Beach and Long Beach around 1978. Through the 1980s it spread to the hardcore scenes of Washington, D.C., Boston and New York where it developed local variants. In New York, the crossover between the city's hardcore scene and its metal scene led to moshing incorporating itself into metal beginning around 1985. In the 1990s, the success of grunge music led to moshing entering mainstream understanding and soon being incorporated into genres like electronic dance music and hip hop.

Due to its violence, moshing has been subject to controversy, with a number of concert venues banning the practice, and some musicians being arrested for encouraging it and concertgoers for participating.

The name "mosh" originates from the word "mash". While performing their song "Banned in D.C." in either 1979 or 1980, H.R., vocalist of Washington D.C. hardcore band the Bad Brains, shouted "mash it - mash down Babylon!" Because of his Jamaican accent, some audience members heard this as "mosh it - mosh down Babylon". Beginning around 1983, metalheads began to refer to the slower sections of hardcore songs as "mosh parts", while hardcore musicians had called them "skank parts". Once Stormtroopers of Death released their debut album Speak English or Die in 1985, which included the track "Milano Mosh", the term began being applied to the style of dance. The term was then further popularised by Anthrax's 1987 song "Caught in a Mosh".

The direct predecessor to moshing was the pogo, a style of dance done in the 1970s English punk rock scene, in which crowds members would jump up and down while holding their arms beside them. According to The Filth and the Fury, it was invented by Sex Pistols bassist Sid Vicious in 1976.

As a prominent punk rock scene in Southern California began to form in the late 1970s and early 1980s with early hardcore punk groups like Fear and Black Flag, moshing as it is understood today began to develop, originally termed "slam dancing". Participants in slam dancing at this time modified the pogo by bringing additional physical contact to those around them by pushing and running, as well introducing the idea of a recognised area where it takes place called a "pit". According to Steven Blush's book American Hardcore: A Tribal History (2001), there is a common belief amongst those involved in this scene that the dance was invented by former US marine Mike Marine in 1978. His specific style, involving "strutting around in a circle, swinging your arms and hitting everyone within reach", would go on to be termed "the Huntington Beach Strut". The Orange County Register writer Tom Berg credited, Costa Mesa venue, the Cuckoo's Nest (1976–1981) as the "birthplace of slam dancing". Examples of this early moshing were featured in the documentaries Another State of Mind, Urban Struggle, the Decline of Western Civilization, and American Hardcore. Fear's 1981 musical performance on Saturday Night Live also helped to expose moshing to a much wider audience.

By 1981, slam dancing had become the predominant style of crowd interaction in the southern California scene, as Huntington Beach and Long Beach became the scene's heart. Washington, D.C. band the Teen Idles toured California in August 1980, where they were first exposed to slam dancing. Upon returning home, they introduced the practice to the Washington, D.C., hardcore scene. That particular scene took a more chaotic approach to slam dancing and saw an increase in stage diving, whereas in the Boston hardcore scene slam dancing became violent and incorporated punching below the neck, developing a style called the "Boston thrash" or "punching penguins". Another development in the Boston scene was "pig piles" in which one person was pushed to the ground and others would begin to pile on top of them. This originated during a D.O.A. set, which was initiated by SSD guitarist Al Barile. The New York hardcore scene of the mid-1980s, modified this early slam dancing into an additional, more violent style. In their distinction, participants may stay in one position on their own or collide with others, while executing a more exaggerated version of the arm and leg swinging of California slam dancing.

As fans of heavy metal music began to attend New York hardcore performances, they developed their own style of dancing based on New York hardcore's style of slam dancing. It was this group, particularly Scott Ian and Billy Milano who popularised the word "moshing". Ian and Milano's band Stormtroopers of Death released their debut album Speak English or Die in 1985, which included the track "Milano Mosh". This led to the term being applied to the style of dance. The same year, moshing began to incorporate itself into live performances by heavy metal bands, with one early example being during Anthrax's 1985 set at the Ritz.